Obstructive sleep apnea is known to cause high blood pressure, snoring and daytime sleepiness, among other issues. Now research studies from Spain indicates that the CPAP mask used to treat it could reduce the risk of developing that high blood pressure and the health hazards that accompany it.

The researchers looked at use of the continuous positive airway pressure (CPAP) mask in two groups with sleep apnea to see whether the individuals developed hypertension.

The study results, just out in the Journal of the American Medical Association, showed that people who use CPAP for four hours or more a night developed hypertension at lower rates than those who were not prescribed CPAP or who used it less.

An explanation of sleep apnea on the Mayo Clinic website notes that the disorder's primary feature is repeated stops and starts to breathing while one sleeps. It's potentially very serious. Symptoms include snoring loudly and feeling tired after a full night's sleep. The Spanish researchers studied the most common form, obstructive sleep apnea (OSA). It occurs when the throat muscles relax too much.

The forced air of the CPAP mask acts as a positive pneumatic splint to hold the airway open. OSA affects 3 to 7 percent of the population.

"CPAP seems to have a protective effect in patients who use the machine properly," Dr. Jose Marin, director of the Sleep Respiratory Unit at Miguel Servet University Hospital in Zaragoza, Spain, and a study author, told HealthDay.

He said that wearing the mask fewer than four hours a night is not considered to be effective, but some patients complain it is too inconvenient, or too noisy or too uncomfortable.

Sleep specialist Dr. Yosef P. Krespi, of Lenox Hill Hospital in New York City, told WebMD that patients could probably overcome those issues if clinicians worked with them. As many as half who try CPAP abandon it after a few days or weeks, the online health news source said.

"We used to tell patients who said they couldn't use CPAP not to worry about it," Krespi said. "Now we tell them to come back in and we work with them. We can readjust the pressure, change the mask, and even add a humidifier if it is too hot. We can do a lot of tweaking."

Other treatments, including surgery or mouth devices, have not proven to be as effective and data is not as strong that they can reduce the risk of high blood pressure, Dr. Aneesa Das, assistant director of the sleep disorder program at Ohio State University, told HealthDay.

In one of the studies, 1,900 people at Marin's clinic without high blood pressure, average age 50, were followed for 11 years with annual blood pressure checks. They found those with sleep apnea who used the mask were 29 percent less likely to develop hypertension during the study than the control group, which didn't have sleep apnea or wear the CPAP mask. They were all snorers, though, with cardiovascular problems. They also saw that patients with apnea who didn't use CPAP developed high blood pressure at higher rates than the CPAP-using group.

They said that differences such as weight, alcohol use or existing blood pressure levels when the study began did not explain the difference in the results.

For the other study, the researchers randomly assigned 725 patients with sleep apnea but not daytime sleepiness to use the mask or not use it. They tracked their blood pressure for about four years and again found those using the mask for at least four hours a night were 28 percent less apt to develop high blood pressure than the others.

The researchers noted the studies did not, however, prove cause-and-effect between CPAP use and reduced risk of high blood pressure, though they believe the association is evident.

Still, wrote Dr. Vishesh K. Kapur and Dr. Edward M. Weaver of the University of Washington Seattle in an editorial accompanying the study in the journal, "Despite these questions, considerable evidence supports the role of identification and treatment of OSA to improve symptoms, quality of life and cardiovascular end points. More specifically, data generally support a causal link with hypertension. Treatment may not only reduce blood pressure (although modestly on average), but if confirmed by future studies also may prevent hypertension in at-risk patients. Thus, OSA deserves attention in patients with or at risk of developing hypertension as a potentially treatable cause of hypertension as well as other clinically important outcomes."